The present invention relates to a scale, especially of the type for weighing human beings, having a tension link plate with at least one stress-dependent resistor bonded thereto for generating an electrical signal that is proportional to the weight of the load applied to the scale.
It is well known in the art to have weighing platforms operatively connected with one or more stress-dependent transducers that serve as weight measuring elements. The stress-dependent transducers or strain gauges are made of electrically conductive wire, etched metal foil, or semiconductor material mounted on deformable strip-like carriers which become elongated as a load is applied to the platform. As the strain gauge carrier elongates, the electrical resistance of the conductive wire, etched metal foil, or semiconductor material changes. Specifically, the electrical resistance increases in proportion to strain produced by stresses imposed on the device. This resistance can be detected by means of a suitable circuit and calibrated in weight units.
In addition to the strain gauge transducers, mechanical guide elements are provided to allow the weighing platform to be vertically displaced. For example, U.S. Pat. No. 3,797,593 issued to Conley shows a plurality of mechanical guide elements each including a tension link captively retained on a cross pin and connected to transducers by attachment to the legs of a clevis by a pin. The base of each of the load transducers is further mounted to mechanical guide elements which are tension coupled to the weighing platform.
A large number of cross pins are used with the mechanical guide elements to provide for connection of all the mechanical guide elements in series to permit the tension produced by the load to be transmitted to the transducer. A first cross pin is supported by upright members of a mechanical guide for the transmission of loads to ground. This first cross pin also supports a means for applying a pure tension load on the transducer and to eliminate any other loads on the transducer. A similar means applies tension to the bottom of the transducer and is coupled to a second cross pin. The second cross pin, in turn, is load coupled to a pair of arms which suspend from a platform. U.S. Pat. No. 4,211,296 issued to Lotscher discloses a scale having an electrical conductor which is displaced in similar fashion to strain gauge conductors and which is deformably placed in tension by holders attached to the wire and to the platform when a load is applied to the platform. U.S. Pat. No. 3,831,687 issued to Maffia et al. discloses a weighing scale wherein a strain gauge load cell is supported in such a manner that a tensile force is applied to it by a support cable.
The prior art scales generally show resistance strain gauges used with mechanical guide elements requiring multiple connections to transfer lever arms, to load links, to bell cranks that allow the application of turning moments correlative with the weight of the load, to clevis and pins and to independently held electrically elongatable wire in order to produce weight measurements of the applied load.
It is therefore an object of this invention to provide an improved tension link having one point of connection directly to a mechanical guide element and another point of connection directly to transfer lever arms.
Another object of the invention is to provide an inexpensive, elastically deformable, thin sheet metal tension link for supporting at least one resistance strain gauge transducer.
A further object of the invention is to provide a single tension link between the applied resultant force and ground so that the resultant force will be directly transmitted to the strain gauge transducers to provide greater accuracy.